1. Field of the Invention
The present invention relates generally to disk drives. More particularly, the present invention relates to a system and method for fail-over switching in a disk storage medium.
2. Background Information
Standard communication between a host computer, such as PC-based computer, and a hard disk drive is conventionally performed using a disk drive host interface. The hard disk drive can be, for example, an Integrated Drive Electronics/Advanced Technology Attachment (IDE/ATA)-compliant hard drive, a SCSI-compliant hard drive, a fiber channel device (e.g., one or more hard drives used with associated fiber channel switches in a multi-disk environment), or any other type of hard disk drive or storage systems.
Many disk drive systems rely upon standardized buses to connect the disk drive host interface to the disk drive. Generally speaking, the computer's operating system accesses a hard disk drive as an input/output (I/O) device connected to a bus, such as the IDE/ATA, SCSI or fiber channel bus. To communicate between the host computer and the hard disk drive via a standard bus, information is transferred to and from the hard disk drive via the disk drive host interface using a standard disk drive host interface protocol. Such an information transfer vests control with the operating system, and the hard disk drive serves as a slave to the host computer. Command signals are supplied by the host computer to the hard disk drive via the disk drive host interface, such that the host computer controls read and write operations for transferring data from or to the hard disk drive.
Failures at the disk drive or at the disk drive host interface can result in the disk drive system going offline. The resulting loss of connection can affect system throughput performance and user application performance.
Fail-over is a backup operation that automatically and transparently switches to a standby connection if a primary host or connection fails and redirects requests from the failed or downed system to the backup system. For example, SCSI and fiber channel buses support a feature that allows them to be accessed by redundant host systems. This feature protects them from losing access to a group of disk drives as a result of a single failure. The fail-over feature is handled by the host computer, i.e., is host-driven.
U.S. Pat. No. 5,922,077, which is hereby incorporated by reference in its entirety, discloses a fail-over switching system. The switching system includes a fail-over switch in a data storage system having multiple storage device controllers separately communicating over redundant fiber channel loops such that if a fiber channel loop becomes disabled, the affected data storage device controller may reroute its communications by sharing the alternate fiber channel loop.
The SCSI and fiber channel host-driven dual-initiator model involves using multiple storage device controllers for each disk drive to maintain plural, independent, continuously-active channels. A SCSI, host-driven, dual-initiator model for performing fail-over is disclosed in U.S. Pat. No. 6,009,535, which is hereby incorporated by reference in its entirety.
It would be desirable to provide a disk drive fail-over protocol using redundant host connections.